Washing machine with drying function

ABSTRACT

A washing machine with a drying function includes a water tub, a rotating tub mounted in the water tub so as to be rotatable, a driver rotating the rotating tub, a circulation passage defined so as to communicate with the water tub, a warm-air supply unit circularly supplying warm air through the circulation passage into the water tub and the rotating tub, a water-supply unit supplying water into the water tub, a control unit controlling the driver, the warm-air supply unit and the water-supply unit thereby to be capable of controlling wash, rinse, dehydration and drying steps, and a preheating unit executing a preheating operation in which warm air is supplied into the water tub and the rotating tub during rotation of the rotating tub before the wash step is executed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2005-12671, filed on Jan. 20,2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing machine having a dryingfunction and provided with a warm-air generator.

2. Description of the Related Art

A drum washing machine with a drying function can provide effectivewashing action while reserving a relatively smaller amount of water in alower interior of a water tub or drum, for example. Accordingly, theaforesaid drum washing machine can achieve water saving. Furthermore,laundry is vertically moved in a drum when the drum is rotated. Whenwarm air is supplied into the drum, the entire laundry can efficientlybe dried while being agitated. The above-described type drum washingmachine with the drying function has recently been diffused rapidly.

On the other hand, in order that a sufficient cleaning performance maybe achieved from a small amount of wash water, some types of theforegoing drum washing machines have recently been designed so that washwater is warmed to accelerate activation of enzyme contained in adetergent. A method of warming wash water includes heating wash water bya sheathed heater disposed on a bottom of a wash tub, and introducing,into a drum, warm air produced by a warm-air supplier comprising a fanand a heater so that wash water is heated. JP-A-2-277494 discloses theconstruction of a drum washing machine of the aforesaid type, forexample.

However, in the aforesaid method using the sheathed heater, on one hand,the sheathed heater disposed in the water needs to be provided with asafety arrangement against electric leakage. On the other hand, in themethod using the warm-air supplier, both wash water and warm air arefluid and accordingly, thermal conduction from warm air to wash waterhas a low efficiency, whereupon it takes a lot of time to warm overallwash water in the drum.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a washingmachine with a drying function, in which wash water can be heated by asimple construction efficiently.

The present invention provides a washing machine with a drying function,comprising a water tub, a rotating tub provided in the water tub so asto be rotatable, a driver rotating the rotating tub, a circulationpassage defined so as to communicate with the water tub, a warm-airsupply unit circularly supplying warm air through the circulationpassage into the water tub and the rotating tub, a water-supply unitsupplying water into the water tub, a control unit controlling thedriver, the warm-air supply unit and the water-supply unit thereby to becapable of controlling wash, rinse, dehydration and drying steps, and apreheating unit executing a preheating operation in which warm air issupplied into the water tub and the rotating tub during rotation of therotating tub before the wash step is executed.

The preheating operation is carried out before the wash step is carriedout and when no water is reserved in the water tub. Accordingly, warmair is supplied into the water tub and the rotating tub so that heat isdirectly applied to laundry, the water tub and the rotating tub. Waterreserved in the water tub in the wash tub subsequently to the preheatingis warmed by making use of heat stored in the laundry, water tub androtating tub by the preheating. Consequently, heat can be conducted fromthe warm air to water in the water tub more efficiently as compared withthe construction that water in the water tub is directly heated by warmair.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome clear upon reviewing the following description of the embodimentwith reference to the accompanying drawings, in which:

FIG. 1 is a schematic front view of a drum washing machine with a dryingfunction in accordance with a first embodiment of the present invention;

FIG. 2 is a schematic block diagram showing an electrical arrangement ofthe washing machine;

FIG. 3 is a flowchart showing a washing operation;

FIGS. 4A to 4C illustrate water levels in a water tub and motion oflaundry in a preheating, preliminary washing and main washingrespectively;

FIG. 5 is a graph showing the relationship between an amount of laundryand a water temperature, a temperature in a water tub and a targetlaundry temperature;

FIG. 6 is a view similar to FIG. 1, showing a second embodiment of theinvention;

FIG. 7 is a view similar to FIG. 4A; and

FIG. 8 is a graph showing the relationship between an amount of laundry,and a temperature in a water tub and a target laundry temperature in amodified form of the first embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the present invention will be described withreference to FIGS. 1 to 5. Referring to FIG. 1, a washing machine with adrying function includes a generally cylindrical water tub 1 and agenerally cylindrical rotating tub or drum 2 mounted in the water tub.The water tub 1 is elastically supported by elastic supporting units(not shown). The water tub 1 is substantially non-porous and accordinglyenables to reserve water. The drum 2 serves as a washing tub,dehydrating tub and drying tub and has a number of through-holes 2 aformed through a circumferential wall thereof. The drum 2 further has aplurality of baffles (not shown).

A brushless DC motor 3 of the outer rotor type (serving as a driver) ismounted on a left side of the water tub 1, for example. The motor 3 hasa rotational shaft 3 a horizontally extending through a hole (not shown)of the water tub 1 to be connected to a central left side of the drum 2.Thus, the drum 2 is rotated with a rotor (not shown) of the motor 3. Asupport shaft 2 b coaxial with the rotational shaft 3 a protrudes from aside of the drum 2 opposed to the motor 3 and is rotatably supported onthe corresponding side of the water tub 1. The drum 2 is thus rotatedabout a substantially horizontal axis.

The water tub 1 has a peripheral wall including an upper part formedwith an access opening (not shown) through which laundry is put into andtaken out of the drum 2. The drum 2 has an opening (not shown)corresponding to the access opening. The drum 2 is controlled so asnormally to stop with the opening being located at an upper part of thedrum so that laundry can be put into and taken out of the drum 2 throughthe upper part of the drum.

A circulation passage 4 with a duct structure is defined on the right ofthe water tub 1. The water tub 1 has a warm-air outlet 1 a formedthrough a lower right portion thereof. The circulation passage 4 has oneend connected to the warm-air outlet 1 a. The water tub 1 also haswarm-air inlets 1 b formed through a potion of the water tub 1 aroundthe support shaft 2 b mounted on the right side of the water tub. Thedrum 2 also has openings 2 c formed through a portion of the drum 2around the support shaft 2 b so that the openings correspond to thewarm-air inlets 1 b respectively. The circulation passage 4 has theother end connected to the warm-air inlet 1 b.

A water-cooled heat exchanger 5 is provided in the middle of thecirculation passage 4. A water pouring unit 6 is provided in an upperportion of the heat exchanger 5 for pouring water into an interior ofthe heat exchanger. A blowing fan unit 7 and a heater unit 8 areprovided in an upper interior of the circulation passage 4 located overthe heat exchanger 5. When the blowing fan unit 7 and the heater unit 8are driven, air in the circulation passage 4 is heated so that warm airis produced. The warm air is caused to flow in a direction of arrow A inFIG. 1 by the blowing action of the blowing fan unit 7 to be suppliedthrough the warm-air inlets 1 b and openings 1 c into the water tub 1and the drum 2. The warm air supplied into the drum 2 flows through theholes 2 a into the water tub 1, returning through the warm-air outlets 1a into the circulation passage 4. The warm air is then caused to flowupward through the heat exchanger 5. Thus the warm air is circulatedrepeatedly. The blowing fan unit 7 and heater unit 8 serve as warm-airsupply unit in the embodiment.

A drain hole 9 is formed in the bottom of the water tub 1. A drain hose10 is connected via a drain valve 11 to the drain hole 9. An overflowport 12 is formed in the right side of the water tub 1 so as to belocated below the warm-air inlet 1 b. An overflow hose 13 is connectedto the overflow port 12. The overflow hose 13 is further connected tothe drain hose 10 downstream with respect to the drain valve 11.

A temperature sensor 14 is mounted on a portion of the right side innerface of the water tub 1 located just over the overflow port 12. Thetemperature sensor 14 comprises a thermistor and detects a temperaturein the water tub 1. Another temperature sensor 15 is provided in thelower interior of the heat exchanger 5. The temperature sensor 15 alsocomprises a thermistor and detects a temperature of water supplied fromthe water pouring unit 6. The temperature sensor 14 serves as a laundrytemperature sensor, whereas the temperature sensor 15 serves an ambienttemperature sensor.

FIG. 2 shows an electrical arrangement of the washing machine. A controldevice 20 comprises a microcomputer and serves as a control unit forcontrolling an overall operation of the washing machine and a preheatingunit. Connected to the control device 20 are a switch input section 21,a water level sensor 22, a rotation sensor 23 and the aforesaidtemperature sensors 14 and 15. The switch input section 21 delivers adetection signal (operation signal) according to an amount of operationof an operation switch (not shown). The water level sensor 22 delivers adetection signal according to a water level in the water tub 1. Therotation sensor 23 delivers a detection signal according to a rotationalspeed of the motor 3.

The motor 3 is connected via an inverter circuit 24 to the controldevice 20. A water-supply valve 26 (a water-supply unit), a heaterelement 27, a fan motor 28, the drain valve 11 are connected via a drivecircuit 25 to the control device 20. The water-supply valve 26 switchesa water supply path between a water-supply path extending from a tap(not shown) of the water service to the water pouring unit 6 and awater-supply path extending from the tap to the water tub 1. The heaterelement 27 constitutes the heater unit 8, and the fan motor 28constitutes the blowing fan unit 7. The control device 20 controls themotor 3, water-supply valve 26, heater element 27, fan motor 28 anddrain valve 11 based on a control program previously stored therein.

The operation of the washing machine will now be described. FIG. 3 is aflowchart showing processing for a standard washing/drying operation.Upon start of operation, the drain valve 11 is opened so that a drainingoperation is carried out (step S1). Consequently, even when water ispresent in the water tub 1 upon start of the operation, all the water isdischarged from the water tub 1. At subsequent step S2, the weight oflaundry in the drum 2 is detected. Subsequently, the water-supply valve26 is switched at step S3 so that the water-supply path leading to thewater pouring unit 6 is opened. As a result, the water pouring unit 6starts a water pouring operation. Since the drain valve 11 is open inthis case, water supplied into the heat exchanger 5 is discharged fromthe drain hole 9 without being reserved. At step S4, the drum 2 isrotated, for example, at 400 rpm. At step S5, the heater element 27 andthe fan motor 28 are energized, so that warm air flows through thecirculation passage 4 to be supplied into the water tub 1.

The steps S3, S4 and S5 are carried out substantially simultaneously.More specifically, warm air is circulated through the circulationpassage 4 supplied with water and the rotating drum 2. Consequently,moisturized warm air is supplied into the drum 2 and the water tub 1 sothat heat is applied to laundry in the drum 2 as well as to the drum 2and the water tub 1. Accordingly, the treatment at steps S3 to S5constitutes a preheating. Since the drain valve 11 is open in thepreheating operation, water is discharged through the drain hole 9without being reserved. Accordingly, a part of the circulation passage 4near the warm-air outlet 1 a can be prevented from being closed bywater, or water can be prevented from entering the drum 2.

A rotational speed of the drum 2 at step S4 is set to about 400 rpm inthe embodiment. The reason for this setting is as follows: an experimentconducted by the inventors shows that a centrifugal force starts actingupon laundry and warm air in the drum 2 when a rotational speed of thedrum 2 exceeds about 300 rpm and that the centrifugal force moveslaundry in the drum uniformly to an inner peripheral surface of the drum2 as shown in FIG. 4A when the rotational speed of the drum 2 rangesfrom 400 rpm to 500 rpm (symbol “W” in FIG. 4 designates laundry)Furthermore, warm air flowing into the central interior of the drum 2 isalso caused to flow toward the peripheral wall of the drum 2 by thecentrifugal force as shown by arrow in FIG. 1B. On the other hand, noiseis produced when the rotational speed of the drum 2 exceeds about 400rpm. In view of the above drawback, the rotational speed of the drum 2is set so that warm air is blown against the whole laundry uniformlywhile noise production is restrained.

The above-described preheating finishes when the temperature of laundryin the drum 2 has reached a target temperature. The control device 20reads the detection signals of the temperature sensors 14 and 15 duringthe preheating operation. The control device 20 estimates a targettemperature of the laundry based on the read detection signal of thetemperature sensor 14. Furthermore, the control device 20 is arranged tochange the target temperature of laundry according to an amount oflaundry and the detection signal of the temperature sensor 15. Therelationship among the target temperature of the laundry, the amount oflaundry and detection temperatures of temperature sensors 14 and 15 willbe described later.

Upon completion of the preheating operation, the control device 20advances to step S6 to execute a first water-supply. The water-supplyvalve 26 is switched in the first water-supply so that the water-supplypath from the tap to the water tub 1 is opened, whereupon water issupplied into the water tub 1. In this case, water is adapted to besupplied through a detergent case (not shown) into the water tub 1. As aresult, detergent contained in the detergent case is supplied into thewater tub 1 with the water. The first water supply is carried out untila water level as shown by “L1” in FIG. 4B is reached in the water tub 1.The water level L1 is previously set according to an amount of laundrydetected at step S2. The drum 2 is rotated at low speeds (40 rpm, forexample) repeatedly alternately in the normal and reverse directions,whereby preliminary washing is carried out. As a result, laundry in thedrum 2 is lifted up by baffles and caused to fall down, so that thelaundry is tumbled repeatedly thereby to be cleaned.

The water level L1 for the preliminary washing is set to be lower than awater level of normal washing. Accordingly, wash liquid made bydissolution of detergent into water in the water tub 1 has a higherdensity than usual wash liquid. Furthermore, the temperature of thewater supplied into the water tub 1 is increased by heat stored in thelaundry, water tub 1 and drum 2 heated by the preliminary washing.Consequently, a high cleaning action can be obtained from thepreliminary washing.

Upon completion of the preliminary washing, the control device 20advances to step S8 to execute a second water supply. In the secondwater supply, water is added into the water tub 1 so that a water levelL2 as shown in FIG. 4C is reached in the water tub 1. The water level L2is previously set according to an amount of laundry detected at step S2and corresponds to a water level in the normal washing operation. Atstep S9, the drum 2 is rotated at a low speed (40 rpm, for example)repeatedly alternately in the normal and reverse directions so that amain washing is executed. As a result, laundry in the drum 2 is liftedup by baffles and caused to fall down, so that the laundry is tumbledrepeatedly thereby to be cleaned. Since the water level in the mainwashing is set to the normal water level as described above, a normalcleaning action can be obtained. When the water level in the water tub 1is reduced below L2 for the reason of absorption of water by laundry orthe like, water is supplied into the wash tub 1 for compensation untilwater level L2 is reached.

The above-described steps S6 through S9 constitute a wash step in theembodiment. Upon completion of the main washing, the drain valve 11 isopened so that water is discharged from the water tub 1 (step S10).Successively, the drum 2 is rotated at high speeds, for example, 800 rpmso that laundry is centrifugally dehydrated (step S1). Subsequently, arinse step (step S12), dehydration step (step S13) and drying step (stepS14) are sequentially executed and thereafter, the washing operation iscompleted. In the drying step, the heater element 27 and fan motor 28are energized and the water pouring operation is carried out by thewater pouring unit 6 in the same manner as in the preliminary washing.As a result, warm air supplied into the drum 2 absorbs moisture fromlaundry. The warm air containing moisture is dehumidified by the heatexchanger 5 and heated by the heater unit 8 again. The warm air isreturned into the drum 2 so that laundry is dried.

The following describes the relationship among a target laundrytemperature, an amount of laundry and temperatures detected by thetemperature sensors 14 and 15 in the preheating operation. FIG. 5 showsthe relationship among a water temperature detected by the temperaturesensor 15, a temperature in the water tub 1 detected by the temperaturesensor 15 and a target temperature of laundry, for every amount oflaundry. The target temperature of laundry is set in a range from 45° C.to 55° C. according to a water temperature as shown in FIG. 5. Thetarget laundry temperature is thus set in order that a proteincomponent, such as blood, milk or egg, which is one of soil componentsadherent to laundry may be prevented from being hardened by thepreheating operation. Since the protein component is hardened at about60° C., the target temperature is set so as to be lower than 60° C. sothat the protein component can be prevented from being hardened,sticking to a fiber of laundry. Secondly, the target laundry temperatureis set in the above-described manner in order that a temperaturedifference between laundry and water supplied into the water tub 1 inthe first water supply may be rendered small for prevention of clothshrinkage of laundry. A temperature of water supplied into the water tub1 in the first water supply is substantially equal to a watertemperature detected by the temperature sensor 15 in the preliminarywashing. Accordingly, a target temperature is set to be low when thewater temperature detected by the temperature sensor 15 is low, whereasthe target temperature is set to be high when the detected watertemperature is high.

Furthermore, the control device 20 estimates a target temperature oflaundry from the water-tub interior temperature detected by thetemperature sensor 14. The relationship between the water-tub interiortemperature and the laundry target temperature was obtained from anexperiment conducted by the inventor. Accordingly, when the temperaturedetected by the temperature sensor 14 has reached the water-tub interiortemperature as shown in FIG. 5, the control device 20 determines thatthe laundry has reached a target temperature, finishing the preliminaryheating. A target temperature of laundry is higher by 2° C. to 15° C.than the water-tub interior temperature as shown in FIG. 5. It isconsidered that warm air flows through the warm-air inlet 1 b into thewater tub 1 and drum 2 during the preheating and the temperature of warmair is detected by the temperature sensor 14 after heat has beenabsorbed by laundry, water tub 1 and drum 2. Accordingly, the differencebetween the laundry temperature and the temperature detected by thetemperature sensor 14 tends to be larger as an amount of laundry islarge.

According to the foregoing embodiment, the preheating is carried outwhen no water is reserved in the water tub 1 before execution of thewash step. In the preheating, warm air is supplied into the drum 2 sothat laundry, water tub 1 and drum 2 are heated. Water reserved in thewater tub 1 is heated in the wash step by making use of heat stored inthe laundry, water tub 1 and drum 2 as the result of the preheating.Consequently, heat can be transferred from warm air to the water in thewater tub 1 more efficiently as compared with the construction thatwater in the water tub is directly heated by warm air.

Furthermore, the preheating is carried out making a direct use of theheater unit 8 and blowing fan unit 8 which constitute the dryingfunction of the washing machine. Accordingly, since no new equipment isnecessitated for the preheating, the construction of the washing machinecan be prevented from complication and the production cost of thewashing machine can be prevented from increase.

Water is poured by the water pouring unit 6 in the reheating so thatwarm air supplied into the water tub 1 is rendered moist. Consequently,laundry can be prevented from being excessively dried in the preheating,whereupon soil can be prevented from becoming difficult to wash off.

The target temperature of laundry, which is a temperature of laundry inthe termination of the preheating, is set to be equal to or lower than60° C. Consequently, the protein component, which is a soil component oflaundry, can be prevented from being hardened. Moreover, the targettemperature of laundry is rendered low when the temperature of water ishigh, whereas the target temperature is rendered high when the watertemperature is high. Consequently, since the temperature differencebetween the laundry heated and the water supplied into the water tub 1is reduced, the laundry can be prevented from shrinkage or damage.

FIGS. 6 and 7 illustrate a second embodiment of the invention. Thefollowing describes only the differences of the second embodiment fromthe first embodiment. In the second embodiment, identical or similarparts are labeled by the same reference symbols as those in the firstembodiment. In the second embodiment, the preheating is executed while asmall amount of water is reserved on the bottom of the water tub 1. Morespecifically, the drain valve 11 is adapted to be closed during thewater pouring in the preheating (see step S3 in the flowchart of FIG.3). Accordingly, water poured into the heat exchanger 5 is reserved inthe circulation passage 4 and also flows through the warm-air outlet 1 ainto the water tub 1 thereby to be reserved in the water tub. The waterpouring is carried out until the water reserved in the water tub 1reaches such a level that the water reserved in the water tub is keptaway from contact with the drum 2 and that the water reserved in thewater tub does not prevent warm air from passing through the circulationpassage 4. The aforesaid water level is designated by symbol “L3” inFIGS. 6 and 7. As the result of the above-described construction, too,moist warm air can be supplied into the water tub 1 in the preheating.

The invention should not be limited to the foregoing embodiments. Theembodiments may be modified as follows. For example, the targettemperature of laundry in the preheating may be constant irrespective ofthe temperature of water poured from the water pouring unit 6 when thewashing machine is installed in an environment where temperature changesare small throughout the year and changes in the ambient temperatureneed not be taken into consideration. In this case, for example, asshown in FIG. 8, it is determined that the laundry has reached thetarget temperature, whereupon the preheating is finished. Thedetermination is based on that the temperature detected by thetemperature sensor 14 has reached a previously determined water-tubinterior temperature previously set for every amount of laundry. Thetemperature sensor 15 may be eliminated in the aforesaid arrangement.

The water pouring by the water pouring unit 6 need not be carried outcontinuously throughout the preheating. The water pouring may be carriedout intermittently or for a short period of the preheating. Furthermore,a water pouring time may be controlled according to an amount of laundryor the like. Consequently, warm air can contain moisture.

The water supply (first water supply) before the preliminary wash may becarried out until a normal water level is reached. The water level isreduced in the first washing operation (that is, the preliminary wash)since the dried laundry absorbs water. Then, additional water supply isusually carried out until a set water level is reached in the middle ofthe washing operation, whereby the lowered water level is returned tothe former state. Accordingly, even when the water level for thepreliminary wash is set to the normal water level, substantially thesame effect can be achieved as the case where the water level is set soas to be lower than the normal water level without execution ofadditional water supply.

The invention may be applied to a washing machine with drying function,which is provided with a rotating tub rotated about a vertical axis.

The foregoing description and drawings are merely illustrative of theprinciples of the present invention and are not to be construed in alimiting sense. Various changes and modifications will become apparentto those of ordinary skill in the art. All such changes andmodifications are seen to fall within the scope of the invention asdefined by the appended claims.

1. A washing machine with a drying function, comprising: a water tub; arotating tub provided in the water tub so as to be rotatable; a driverrotating the rotating tub; a circulation passage defined so as tocommunicate with the water tub; a warm-air supply unit circularlysupplying warm air through the circulation passage into the water tuband the rotating tub; a water-supply unit supplying water into the watertub; a control unit controlling the driver, the warm-air supply unit andthe water-supply unit thereby to be capable of controlling wash, rinse,dehydration and drying steps; and a preheating unit executing apreheating operation in which warm air is supplied into the water tuband the rotating tub during rotation of the rotating tub before the washstep is executed.
 2. The washing machine according to claim 1, whereinthe preheating unit executes the preheating operation while a smallamount of water is reserved in the water tub.
 3. The washing machineaccording to claim 1, further comprising a heat exchanger including awater pouring unit provided midway in the circulation passage forpouring water for dehumidification of air passing through thecirculation passage, wherein the preheating unit executes the preheatingoperation when the water pouring unit has poured water.
 4. The washingmachine according to claim 1, wherein the wash step includes a main washand a preliminary wash carried out while water whose amount is smallerthan in the main wash is reserved in the wash tub.
 5. The washingmachine according to claim 1, further comprising a laundry temperaturesensor detecting a temperature of laundry in the rotating tub, whereinthe preheating unit executes the preheating operation until thetemperature of laundry reaches a previously set target temperature. 6.The washing machine according to claim 5, wherein the target temperatureis set to 60° or below.
 7. The washing machine according to claim 5,further comprising an ambient temperature sensor detecting an ambienttemperature, wherein the target temperature is changed according to theambient temperature.